Ni/ZSM-22 Zeolites On Hydroisomerization Performance For F-T Heavy Diesel

Fischer-Tropsch synthetic oils are mainly long-chain paraffins and have the advantages of no sulfur,no nitrogen and low aromatics.They can be used as raw materials for high-grade diesel and lubricating base oils.However,long-chain alkanes have higher freezing points and poor low-temperature fluidity,which requires heterogeneous pour point depressing to improve their oil properties.Based on this,this project is oriented towards industrial development,combined with the sulfur-free cleaning advantages of Fischer-Tropsch synthetic oils.By screening industrially produced zeolites acid materials and matching with metal components,a long-chain normal paraffin is developed.It has high isomerization activity and good selectivity,and is suitable for the non-sulfurized catalyst of Fischer-Tropsch heavy oil isothermal pour point depressing;and further explains the influence of various properties of the catalyst on the isomerization reaction performance of long-chain alkanes and its mechanism.This project firstly uses metal Pt and Ni as hydrogenation components,and investigates the hydrogenation isomerization properties of acid zeolites(such as ZSM-5,SAPO-11,Beta and ZSM-22 zeolites)commonly used in industry.Molecular sieves of acidity and pore structure are used for the development of heterogeneous pour point depressing catalysts.The results show that compared with other zeolite carriers,the ZSM-22 molecular sieve with a silicon-aluminum ratio of 300 is suitable for one-dimensional ten-membered ring channel structure when the precious metal Pt is used as the active component.Thus,it exhibits the highest hydroisomerization performance,the highest diesel yield and the best pour point depressing effect.Effect of metal sites on the heterogeneous properties of the bifunctional catalyst was investigated based on ZSM-22 zeolites.When metal Ni is used as the active component,the hydroisomerization performance of the metal Ni is weaker than Pt,which results in the inability of the iso-intermediate to be hydrogenated in time,which reduces t:he isomer selectivity and increases the cracking reaction.In order to reduce the cost of the catalyst,the influence of the ratio of silicon to aluminum on the grain morphology,size,acid strength and content of ZSM-22 zeolite was investigated in detail.The F-T heavy diesel oil was used as raw material.The heterogeneous reaction performance of different catalysts.The results show that the silica-alumina ratio has a significant effect on the morphology and acidity of the zeolite crystal.Among them,ZSM-22-70 zeolite with small crystal sizes and low silicon to aluminum ratio is more suitable for the heterogeneous pour point depressing reaction of F-T heavy diesel oil.The Ni-based catalyst(HI-1)developed for its acidic component shows better performance.When the diesel yield of the product is 80%,the cold filter point is-8 ?.Subsequently,by investigating the active metal loading mode of the catalyst,it was found that when the catalyst was prepared by coprecipitation or homogeneous precipitation compared with the impregnation method,the dispersion of the active metal was significantly increased,and the distance between the active site and the acid site of the metal was shortened.In order to improve the compatibility of the hydrogenation-dehydrogenation function of the active metal on the catalyst with the acid function,the isomerization performance of the catalyst is significantly increased.At the same time,the isomerization performance of the catalyst prepared by the homogeneous precipitation method is slightly higher than that of the coprecipitation method,and the condensation point is-8 ? when the diesel yield is 90%.On the basis of the above work,ZSM-22-70 molecular sieve was modified and characterized by ion exchange.Effect of Zn contents on the heterogeneity of the catalyst was investigated.The results show that the specific surface area,pore volume and pore size of the molecular sieve after Zn modification are slightly reduced,but the total acid amount is obviously reduced;and with the increase of ZnO contents,it tends to decrease slightly and then the catalyst active metal The matching of hydrogenation function and acid function is significantly increased,the selectivity of isomerization is increased,and the low temperature flow performance of the diesel fraction can be effectively improved while maintaining high diesel yield.